Error Reporting Communications; Overview Of Initial, Update Copy Operations; Initial Copy; Update Copy - HP StorageWorks P9000 User Manual

Continuous Access Synchronous Z does not provide host-failover functions. Use the failover software
most suitable for your platform and requirements.

Error reporting communications

Error reporting communications (ERC) transfers information between host processors at the main
and remote sites. It is a critical component of a disaster recovery effort.

Overview of initial, update copy operations

When you perform the initial copy operation, all the data in the M-VOL is copied into the R-VOL.
Thereafter, Continuous Access Synchronous Z and the main and remote systems execute update
copy as often as writes are sent by the host. The update operation copies host updates to the R-VOL
at the same time that they are copied to the M-VOL.
The following figure illustrates the initial and the update copy operations.
Figure 2 Remote copy operations

Initial copy

When a new pair is created, the entire contents of the M-VOL are copied to the R-VOL, cylinder
by track (this does not include for diagnostic and unassigned alternate tracks). The initial copy
synchronizes the M-VOL and R-VOL, independently of host I/O processes.
In an initial copy, you can elect to have no data copied if the M-VOL and R-VOL are already
identical. You can also specify options that provide additional flexibility between the speed of
data transfer and system performance.
The copy pace option allows you to specify the maximum number of tracks (1- 1 5) that can be
copied simultaneously before the main system accepts another host request for that M-VOL. If
more tracks are copied, the operation completes more quickly; if fewer tracks are copied,
performance is maintained at a higher level.
The priority option allows you to specify the order in which copying is performed on multiple
pairs. This is used if more pairs are being created than the maximum initial copy activity
setting.
The maximum initial copy activity option allows you to specify the maximum number of
concurrent initial copy and resync copy operations that each main system performs (not
pair-specific).
The Round Trip Time option allows you to specify the time limit for data to travel from the
M-VOL to R-VOL. This value is used by the system to control initial copy pace when update
copying is in progress.
These options are available on Remote Web Console only.

Update copy

If the host issues an update after the initial copy is complete, the data is written to the M-VOL and
copied to the R-VOL. The write operation is acknowledged to the host as complete after the data
is copied to the R-VOL in the RCU.
12 Continuous Access Synchronous Z overview